Manipulation Of Nanoscale Optical Field

With the rapid development of nanophotonics and photonic devices, how to makethe device capable of high capacity, high density, high resolution information transferwill be crucial. For many photonic devices, the size of the focal spot in the system andthe intensity of the optical field determine the minimum feature size and processingresolution.At present, manipulation of the nanoscale optical field mainly has the followingtwo ways: the first is the far field modulation technology which refers to modulatingand filtering the amplitude, phase or polarization of the incident beam before focusingit with traditional microscope objective. Generally, the bigger the numerical apertureof the abjective and the shorter the wavelength, then the smaller the focal spot; thesecond method is the near field focusing technique, namely confining the surfacePlasmon polariton to the near field center through propagating and interference andresulting in the enhanced nanoscale spot. Surface plasmonic lens is the nanostructureswhich focus the surface plasmonic wave propagating along the surface of metal to thenanoscale spot.For the far field modulation techniques, we proposed some modulation methodsand simulated the various focus spots with special shapes which may have importantroles in the practical application. First, we generate the complete spiral focus spot.Because the study of large molecules such as DNA mechanical properties andbiological properties may use laser focusing spot to rotate and stretch, the completespiral focus spot in the manipulation of the DNA will be a potential tool. Secondly, wesimulated multiple split-ring-shaped focusing spot aligned along the optical axis, thusthe axial scanning in fabrication of matematerial using laser direct writing will nolonger be necessary; Third, we proposed a method of creating a super-longmagnetization needle with high aspect ratio by focusing two azimuthally polarizedand azimuthally phase-modulated vortex beams and by connecting two opposingmagnetization needle ends together. At present, a longitudinal magnetization needlewith high aspect ratio has a very important role in the field of atom trapping, spinwave operation, magnetic data storage, and ferromagnetic semiconductor devices etc. But the magnetization needle obtained using electron beam lithography in practicalapplication is very expensive and the near field operation is extremely complex;finally, in the focal volume of a high numerical aperture objective, we defined theazimuthal angle and polar angle of the overall polarization orientation and wecalculated these angles of the electric fields in the focusing spot which aremanipulated by focusing three differently weighted and differently polarized incidentbeams and using the azimuthally adjustable amplitude filter. In three dimensionalfocal volume, the polarization direction and intensity distribution are bothmanipulated.For near field focusing technique, we first proposed an infrared wideband surfaceplasmonic lens used for focusing unidirectional propagation surface plasmonpolaritons. So it is shown that this special nanostructure of surface plasmonic lens willnot couple with nearby nanostructure and cause scattering and detrimental noise whenit is illuminated by a radially polarized beam. The extinction ratio of greater than15in the near infrared wavelength range of about160nm can be realized. it is conduciveto the integration of optoelectronic devices; then we put forward an integratedmultistage nanofocusing system, namely hybrid lens which are composed of atraditional high numerical aperture objective, a surface plasmonic lens andcone-shaped nanoparticles in the center of the lens. In this hybrid lens, near-fieldnanometer focus is generated through three processes: first, a micrometer scale spot isformed by focusing the radial polarized incident beam through the objective; secondly,the surface plasmonic waves excited in the annular slit of the surface plasmonic lensare focused into a highly confined and enhanced nanoscale spot in the center of thestructure; third, the localized surface plasmon polaritons are further excited at the tipof a cone-shapedn nanoparticle by highly confined and enhanced electric field. It isdemonstrated that the full width at half maximum of the spot at the tip of thenanoparticle is as small as20nm and the enhancement factor is5orders of magnitude.